Conventionally, there has been known an image forming apparatus which forms an image on a sheet based on image data and ejects the sheet having the image formed thereon. The image forming apparatus is, for example, a copier, a printer, a facsimile machine, a complex machine or the like. If the image forming apparatus is a copier, it obtains image data by reading an image from a document. On the other hand, if the image forming apparatus is a printer, it obtains image data from an external apparatus such as a personal computer.
A case where an image forming apparatus outputs an output unit composed of a plurality of pages is thought as the use of the image forming apparatus. In such a case, a confirmation operation of confirming whether or not images are normally formed on sheets is important. For example, in the confirmation operation, the presence or absence of page missing and page misplacement is confirmed.
Here, if page missing and page misplacement of an output are manually confirmed after the output in the case of outputting a plurality of sets of output units, particularly in production type printing for mass printing, a huge amount of man-hours are required. If outputs with page missing or page misplacement should be delivered to a client, this results in the considerable loss of the client's trust.
Accordingly, it is preferable to automate the confirmation operation and a technology for detecting page missing at the time of printing has been proposed in patent literature 1, patent literature 2 and the like.
In patent literature 1 is proposed an image forming apparatus in which identification information corresponding to each of a plurality of pages is attached to page data, arithmetic processings dependent on the reading order of the page data are performed, an arithmetic processing result of the nth set and those of the sets other than the nth set are compared to determine whether or not images have been normally formed on a plurality of sheets for the output units other than that of the nth set. Specifically, the absence of page missing, page misplacement and the like is determined if the arithmetic processing results of the sets other than the nth one agree with the arithmetic processing result of the nth set, and the presence of page missing, page misplacement or the like is determined unless the above arithmetic processing results agree.
In patent literature 2 is proposed a technology for comparing the total value of pixel numbers of a plurality of pages constituting the nth set of output unit and that of pixel numbers of a plurality of pages constituting the (n+1)th and subsequent sets of output units (hereinafter, referred to as a first technology). Specifically, an image forming apparatus determines the absence of page missing, page misplacement and the like in the (n+1)th and subsequent sets of output units if the total values of the pixel numbers agree. On the other hand, the image forming apparatus determines the presence of page missing, page misplacement or the like in the (n+1)th and subsequent sets of output units unless the total values of the pixel numbers agree.